1. Field of the Invention
This invention relates to new and useful improvements in the production of sand cores and molds for foundry use and more particularly to resin and catalyst compositions used in the manufacture of sand cores and molds.
2. Brief Description of the Prior Art
The preparation of sand cores and molds for use in foundry operations is a well developed art. In the past, a variety of binders have been used for the preparation of sand cores and molds. Most sand cores and molds today are made using various condensation-type organic resins. The condensation-type organic resins are thermosetting resins and are usually acid-curable, at least under some conditions. Phenolic resins, phenolic modified furan resins, furfuryl alcohol-urea-formaldehyde resins, furfuryl alcohol-formaldehyde resins and furfuryl alcohol-urea phenol-formaldehyde resins are typical of the resins that have been used in the preparation of sand cores and molds for foundry use.
The prior art dealing with thermosetting or condensation-type resins discloses a large number of acid catalysts that have been used for effecting a condensation-type polymerization of resin precursors or monomers. It has been found, however, that all of the acids which are capable of effecting condensation-type polymerization are not equally effective in the preparation of resin-bound sand cores or molds. In fact, many of the acids which are disclosed to be satisfactory catalysts for the curing of condensation-type resins are inoperative to produce satisfactory resin-bound sand cores or molds.
Catalysts which have been used in acid catalysis or acid curing of condensation-type resins include mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc., simple organic acids such as formic acid, acetic acid, trichloroacetic acid, trifuluoroacetic acid, etc., and strong organic acids such as the aromatic sulfonic acids, viz. benzene sulfonic acid, toluene sulfonic acid, zylene sulfonic acid, etc.
In the preparation of sand cores and molds, the various mineral acids and the simple organic acids have proved unsatisfactory for a variety of reasons. The aromatic sulfonic acids have produced satisfactory sand cores or molds but usually require a rather substantial setting or curing time. The sulfonic acids also have the disadvantage that there is a substantial evolution of aromatic hydrocarbons in the emissions from metal casting operations using sand cores or molds where the aromatic sulfonic acids have been used as catalyst for the resin binders. Accordingly, there has been a substantial need for acid catalyst or curing agents for catalysis or curing of condensation-type resin binders for sand cores or molds which will cure in a shorter period of time than the sulfonic acids without substantial reduction in strength or hardness of the sand cores or molds produced using such resins.